STUDY ON ADSORPTION AND DESORPTION OF SOME SOILS

The adsorption and desorption of fluoride on 8 kinds of soils, developed from granite, red sansy-stone and purplish sandy shale, in centre south China were studied.The results indicated that: (1) The trial data of F adsorption on examined soils were significantly conform to Langmuir, Freundlich and Temkin equations. The amount of fluoride adsorbed by soils developed from granite was abviously more than that of soils developed from red sandy stone and purplish sandy stone and purplish sandy shale. (2) The fluoride' adsorbed by soils derived from red sandy stone and purplish sandy shale,and laterltic soil and latosol developed from granite could be completely desorbed by 0. 1 mol/L KOH solution, whereas fluoride adsorbed by yellow brown earth and red earth could be only partly desorbed by it, which is related to more 14nm transitional mineral in yellow brown earth and red earth. (3) The fluoride adsorbed by examined soils could not be completely desorbed by water, and its ratio varied with soil. The rate of fluoride desorbed in soils derived from granite (26. 9%～40. O%) was smaller than that of soils developed from red sandy stone and purplish sandy shale (44. 8%～94. 20%). (4) The differences of characteristics of adsorption and desorption of fluoride among soils used were relative to the type and quantity of soil minerals, especially ferric oxide andalumina.